Dynamic bit rate conversion in multipoint video transcoding

This paper investigates the bit-rate conversion and bit re-allocation for video combining in a Multipoint Control Unit (MCU). To combine the pre-encoded multiple video sequences into a single sequence, the total bit-rate may overwhelm the outgoing channel bandwidth. Instead of multiplexing, we apply the transcoding approach to control the bit-rate and reallocate the bits in order to improve the pictures quality. To speed up the operation, a video transcoder usually reuses the decoded motion vectors to reencode the video sequences. Those decoded motion vectors also serve as a good indication of the picture activities. In this paper we uniformly distribute the bit-rate to the combined sequence and then use the motion information and the Lagrange optimization method to reallocate the bits to each sub-picture. The simulation results show that the PSNR distribution of the sub-sequence is more uniform and the video qualities of the active subsequences are much improved